1. Field of the Invention
This invention relates generally to low fluid loss cement compositions, fluid loss reducing additives and methods of using the cement compositions in well cementing operations.
2. Description of the Prior Art
Hydraulic cement compositions are utilized extensively in the construction and repair of oil, gas and water wells. For example, hydraulic cement compositions are used in primary well cementing operations which involve the placement of a cement composition into the annular space between the walls of the well bore and the exterior of a pipe such as casing disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened impermeable cement therein. The objective of the cement sheath is to physically support and position the pipe in the well bore and bond the pipe to the walls of the well bore whereby the undesirable migration of fluids between subterranean zones or formations penetrated by the well bore is prevented.
In the operation of wells after primary cementing and other completion operations have been accomplished and produced fluids have been recovered from one or more subterranean formations penetrated by the well bore, problems relating to the undesirable flow of fluids with or without fine solids into or from locations in subterranean formations or the well bore often occur. Ordinarily, the undesirable passage of fluids involves the movement of oil, gas or water through small holes or cracks in the well casing and/or through holes, cracks, voids or channels in the annular cement sheath between the casing and the walls of the well bore. The problems of undesirable fluids passing through such openings have traditionally been solved by placing hydraulic cement compositions in the openings followed by permitting the cement compositions to harden and form impermeable plugs therein. These remedial techniques are generally referred to in the art as squeeze cementing.
The success of primary cementing, squeeze cementing and other well cementing operations depend, at least in part, on the ability of the hydraulic cement compositions used to retain fluids, e.g., water, until they have been placed in desired locations in wells. That is, as a cement composition is pumped through the well bore and contacts permeable subterranean formations penetrated thereby, water and other liquids included in the cement composition can be lost to the permeable formations. Since a hydraulic cement composition is basically comprised of a water slurry of cement and other solid particles, when portions of the water forming the slurry are lost, the consistency of the composition is also lost which can prevent the composition from being placed in the intended location, from setting into a hard impermeable mass and from achieving the intended cementing result.
Heretofore, a variety of fluid loss reducing additives have been developed and used in well cement compositions. Such additives reduce the loss of liquids from a cement composition when it is in contact with a permeable surface. Both particulate solid and liquid fluid loss reducing additives have been developed, but liquid additives are generally preferred in that they are more readily measured and mixed with a cement composition. However, when exposed to atmospheric air, prior liquid fluid loss reducing additives have often gelled or formed lumps therein making them difficult to measure and mix. Thus, there is a need for improved liquid fluid loss reducing additives which can be repeatedly exposed to atmospheric air without gelling or forming lumps as well as improved low fluid loss cement compositions containing the additives and methods of use.